Comparative study of micellization and surface properties of cationic and anionic surfactants in acetonitrile–water mixed media Scientific paper

Abstract

A comparative study was conducted to investigate the micellization behaviour, surface properties and wettability of the cationic surfactant cetyltri­methylammonium bromide (CTAB) and the anionic surfactant sodium dodecyl sulfate (SDS) in acetonitrile–water (ACN–water) mixed media. Surface tension and contact angle measurements were performed in pure water and ACN–water mixtures (0.10, 0.20 and 0.40 volume fractions of ACN) at 298.15 K to deter­mine the critical micelle concentration (CMC), surface excess concentration (Γ_max), minimum surface area per molecule (A_min), micellar surface pressure (π_CMC) and packing parameter (P). Contact angle measurements were used to assess wettability on borosilicate glass surfaces. Results indicate that increasing ACN content leads to an increase in CMC, suggesting reduced micellization feasibility in less polar media. Surface excess concentration decreases with higher ACN fractions, while minimum surface area per molecule increases, indicating looser molecular packing at the air/solution interface. Contact angle measurements reveal a decrease in wettability with higher ACN content, dem­onstrating enhanced surfactant adsorption at the solid-liquid interface. Addit­ion­ally, micellar surface pressure and packing parameter decline with inc­reasing ACN concentration. These findings underscore the critical role of sol­vent composition in modifying surfactant aggregation and interfacial behaviour.